Valve solenoid problems 1

[jcaden]

I have a customer that has had 2 sets of valve solenoid coils burn out, repeated in about 6 weeks. These are 4 way, 2 position, double solenoid hydraulic valves. They are PLC output driven thru individual fuses.

I have checked voltage levels, OK. I have made sure both solenoid coils are not energized at the same time. When I check current, it was within manufacturer spec's.
Any ideas on what to check next?

 

[MikeHalloran]

Next questions:
How often are the coils turned ON, how long do they stay ON, and how long are they OFF?

Does the PLC, intentionally or not, drive the coils with a PWM signal?

Are the coils rated for continuous duty, or for the duty cycle that's actually applied?



Mike Halloran
Pembroke Pines, FL, USA

 

[jcaden]

Answers: The valves may be energized for several hours continuously if the machine is in hold position.
During machine operation, they could be on for 10 seconds every 30 seconds. The PLC uses triac outputs to switch 120 VAC to valves. The valves are supposed to be continuous duty.
I rebuilt the machine about 8 years ago, and no problem till now.

 

[MikeHalloran]

Next thing to check is whether some foreign material or wear product or failure detritus or misadjustment is preventing the solenoid plungers from actually bottoming out. (Solenoids held partially open will overheat).



Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

Continuous is easy duty. A rapid duty cycle will cause overheating. Has the duty cycle changed? PWM is not good for a solenoid unless it has been specifically designed for PWM duty. Is it possible that the first replacement was with the cheapest valve instead of an exact replacement?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Triac. Hm.. Working triacs with margint gate current in 1st and 3rd quadrants can be tricky. Especially with inductive load. If triggering fails in 3rd, but works in 1st, you will send DC to the coil and kill it within a minute or less.

Mains voltage distortion, reduced mains voltage, low temperature, other triac, removed snubber, new coil with "better" specs (lower current consumption) are possible reasons for that kind of problem.

Gunnar Englund

http://www.gke.org

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